Fiber Optic Surface Finishing
In general, polishing of fiber optic connectors requires an epoxy removal polish step followed by a rough, intermediate and final polishing step. Silicon carbide (SiC) or alumina (Al2O3) lapping films are typically used for epoxy removal and the rough polishing steps because they are lower cost, although diamond has better performance and is more effective for polishing ceramic ferrule connectors and APC type connectors. For the intermediate and final polishing steps, fine diamond or alumina lapping films are most commonly used. Table I provides a list of the most common abrasives and support surfaces used for polishing fiber optics.
Table I. Range of Fiber Optic Polshing Abrasives
Stage |
Purpose |
Common Abrasive Types |
Support Surfaces |
Lubricants |
| 1st | Epoxy removal | -5 to 30 micron SiC -5 to 20 micron Alumina -3 to 30 micron Diamond |
-40-90 Shore D Rubber pads |
-DI water -Polylube |
| 2nd | Fiber orientation and geometry | -5 to 12 micron SiC -5 to 12 micon Alumina -2 to 12 micron Diamond |
-70 Shore D Rubber pads | -DI water -Polylube |
| 3rd | Geometry | -2 to 5 micron Diamond -0.01 to 3 micron Alumina |
-70 Shore D Rubber pads -Polishing pads |
-DI water -Polylube |
| 4th | Surface finish and final geometry | -0.01 to 1 micron Diamond 0.01 to 0.5 micron Alumina |
-70 Shoe D Rubber pads |
-DI water -Polylube |
Epoxy Removal - Most connectors are still manufactured by aligning the fiber and then ingecting epoxy into the ferrule to hold the fiber in place. After cleaving, the protruding fiber and the excess epoxy are removed by grinding with a lapping film. The use of a 15 micron SiC lapping film for this step is quite common.
Polishing - A rough, intermediate and final polish are use to both shape and produce an optical transparent surface. For curved surfaces lapping films on a Rubber pad (typcially Shore 70 hardness) produce the desired curvature for optimum perfornance. In practice, the polishing procedures are very dependent upon the type of connector as well as the users polishing equipment and polishing parameters.
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| 3D Optical Profile of a Polished Single Mode Connector |
3D Optical Profile of a Polished Multi-cable Connector |